水下超声速燃气射流的初期流场特性研究

针对超声速燃气射流在静水介质中扩展的复杂多相流动问题，在压力水筒中开展了固体火箭发动机水下点火实验；基于雷诺时均Navier-Stokes方法和流体体积模型，对相同工况进行了燃气与水耦合数值求解。研究结果表明：水下燃气射流迅速建立超声速流动后，高速射流的冲击作用导致燃气泡呈现出帽状特征，并逐渐演变为类椭球体的气囊，平均轴向扩展速度约为40 m/s；燃气泡内部流动结构复杂，存在两个剪切涡环与重复出现的激波胞格，射流边界与燃气泡边界的相互作用会导致射流后续演化的不稳定；燃气扩展时通过压力波在水流场中产生高压区，其压力峰值在振荡中逐渐与环境压力匹配，喷管堵盖打开压力、出口截面积是影响推力峰值的重要因素。

Research on the Initial Flow Field Characteristics of Underwater Supersonic Gas Jets

To investigate the complex multiphase flow of supersonic gas jets in still water,an underwater ignition experiment of solid rocket motor is conducted in the pressure tank,and the numerically simulated results of gas-water coupling for the same case are obtained by using Reynolds-averaged Navier-Stokes (RANS) method and volume of fluid(VOF) model.The results show that,after underwater gas jets achieve supersonic flow,the gas bubble appears to be cap-like due to the jet impact effect.Then the gas bubble gradually evolves into an ellipsoid-shaped gasbag with average axial expansion velocity of about 40 m/s.The flow structures inside the gas bubble are very complex,where two shear vortex rings and repeated shock cells exist.The interaction between the boundaries of gas jet and gas bubble may induce the instability of gas jet in the subsequent evolution stage.It is also demonstrated that there exists a part of high pressure in the flow field,and the pressure peaks gradually match with the environmental pressure in the oscillation process.The pressure of opening nozzle closure and the area of nozzle outlet are the two important factors that affects thrust peak value.